The invention relates to a connection piece with a sealing bead.
A valve connection piece that has an annular sealing face with an surrounding sealing bead is already known from high-purity gas technology. A connection nipple, which likewise has an annular sealing face with a surrounding sealing bead, can be connected to this valve connection piece. A sealing ring made of soft metal is arranged between the two sealing faces, so that when the connection nipple is connected to the connection piece the two sealing beads are pressed into the two end faces of the sealing ring. Such a coupling system is standardised by the xe2x80x9cCompressed Gas Association, Inc.xe2x80x9d (USA) under the designation xe2x80x9cOutlet connections for ultra high integrity service, CGA 630/710 seriesxe2x80x9d(see e.g. data sheets xe2x80x9cDrawing No. 630xe2x80x9d, edition: CGA V-1, October 1994). It is characterised by high tightness and reliability and is therefore used in particular for high-purity gases in the semi-conductor industry.
To prevent any risk of a gas leak in the case of highly toxic, corrosive or pyrophoric gases, the sealing bead is subjected to a stringent check. If, for example, a sealing bead on a valve connection exhibits only slight traces of corrosion, small scratches or minimum damage, which may impair the tightness, the valve is not accepted. In most cases refinishing of the standardised geometry of a damaged sealing bead at acceptable cost is not possible, so that the complete valve is replaced. However, it is expensive and time-consuming to replace the valve in the case of high-purity gases. It is an object of this invention to eliminate or reduce these disadvantages.
On a connection piece in accordance with the present invention, the sealing bead is formed by an interchangeable insert, which is placed in a sealed manner into a chamber that opens in an end face of the connection piece. If slight traces of corrosion, scratches or damage to the sealing bead of the connection piece are detected during acceptance of a valve, the insert forming the sealing bead is simply changed. Expensive refinishing of the sealing bead on the connection piece is thus dispensed with. A further advantage of the invention is that the insert can be placed in the connection piece just before delivery of the valve. The invention likewise permits preventive interchange of the sealing bead after a certain operating time or during specific interventions. For example, a new insert can easily be placed systematically in the connection piece of a cylinder valve after filling the cylinder. It should also be emphasised that the use of the connection piece with insert according to the invention does not require any modifications to the connection nipples. In other words the use of the invention does not cause any adaptation costs for the final customer.
As the seal between the insert and connection piece need not be standardised, the valve manufacturer has wide scope to design this seal in such a way that the sealing faces in the connection piece, for example, can easily be refinished after withdrawal of the insert. In a preferred embodiment the seal between the insert and connection piece is effected by an axial sealing ring, preferably a metal sealing ring. The latter rests with its first end face against an easily refinishable annular chamber sealing face in the chamber in the connection piece and with its second end face against an annular second sealing face on the insert, at least the first end face of the sealing ring forming a sealing bead. A second sealing bead can be positioned either on the annular sealing face on the insert or, preferably, on the second end face of the sealing ring.
The axial sealing ring is advantageously placed in a sealing ring chamber open at the end in the insert, this sealing chamber being designed in such a way that its first sealing bead does not project from the sealing ring chamber. Consequently it is ensured that this first sealing bead is largely protected against damage before and during assembly of the insert. The annular chamber sealing face is advantageously surrounded by an annular groove, into which the wall of the sealing ring chamber is inserted, so that this chamber sealing face rests against the first sealing bead of the sealing ring.
The seal between insert and connection piece is advantageously augmented by a radially acting sealing element between a rotation-symmetrical surface in the chamber and a rotation-symmetrical surface on the insert. A secondary radial seal of this kind ensures a minimum tightness between the insert and connection piece, if no connection nipple is connected or if the lafter is not screwed tight enough to ensure the effectiveness of the axial sealing ring. It comprises, for example, an O-ring, which is installed in an annular groove in the chamber of the connection piece in such a way that it is sealed against a cylindrical surface of the insert. Alternatively the O-ring could also be arranged in an annular groove of the insert.
In the chamber the insert is advantageously secured by at least one screw, this screw being screwed into the chamber wall and projecting into the chamber at right angles to the central axis of the connection piece. It interacts with a bevelled surface of the insert in such a way that the insert is blocked by the wedge effect of the bevelled surface in the direction of the chamber opening, but is freely movable in the direction of the chamber sealing face.
In an advantageous embodiment the insert has a first cylindrical guide surface, a tapered clamping surface and a cylindrical sealing face, which are arranged in this order from its end with the first sealing bead to its opposite end. The chamber is then advantageously designed as a stepped bore, the cylindrical guide surface being guided in a first step and the cylindrical sealing face sealed in a second step by a radially acting sealing element, the diameter of the first step being larger than the diameter of the second step.
It should be noted that a flow limiter can advantageously be integrated in the insert.